The invention relates to a method and a control device for position locking of a torque delivering power tool to a certain screw joint or assembled object for guaranteeing correction of an unacceptable screw joint tightening result before moving to the next screw joint or object.
In particular, the invention concerns a method and a control device for a screw joint tightening power tool and by which the power tool operation is locked to the very object or position on the object in which an unacceptable tightening result has been indicated, thereby making sure that a correction of an unacceptably tightened screw joint is not neglected.
A problem occurring at assembly line screw joint tightening is that unacceptably tightened screw joints now and then is left in that state without being corrected. Due to stress and/or lack of attention operators may leave screw joints as acceptably tightened despite the power wrench system has indicated NOK (not o.k.). This error indication means that there is some faulty with a screw joint or with the power wrench, and that a desired tightening level has not been reached and that the obtained tightening result does not lie within acceptable angle and/or time limits. A screw joint which has not been acceptably tightened may result in a weaker assembly with hazardous results at future use, for instance a break down of safety critical parts of a motor car. A NOK indication should result in correction measures being taken including checking the screw joint for damaged parts and/or checking the power wrench for malfunction, and followed by exchange of damaged screw joint parts and/or shifting to a properly functioning power wrench and retightening of the screw joint to an acceptable result.